/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.flink.api.common.typeutils;

import org.apache.flink.annotation.Internal;

/**
 * This interface defines the method required by the runtime to use data types in join-like operations.
 * In such operations, instances of different data types are compared for equality with respect to certain
 * attributes, such as join keys.
 * 
 * The class compares instances of two different data types. One is always used as the reference data type,
 * and the other is checked against the reference. An instance of the reference data type is normally set as the
 * reference for comparisons. Afterwards one or more instances of the other data type are checked against the
 * reference.
 * 
 * @param <T1> The class of the first data type.
 * @param <T2> The class of the second data type. 
 */
@Internal
public abstract class TypePairComparator<T1, T2> {
	
	/**
	 * Sets the reference for comparisons.
	 * 
	 * @param reference The reference instance.
	 */
	public abstract void setReference(T1 reference);
	
	/**
	 * Checks, whether the given candidate instance is equal to the reference instance, with respect
	 * to this comparator's equality definition.
	 * 
	 * @param candidate The candidate to check.
	 * @return True, if the candidate is equal to the reference, false otherwise.
	 */
	public abstract boolean equalToReference(T2 candidate);
	
	public abstract int compareToReference(T2 candidate);
}
